Polyester modification method

ABSTRACT

The subject invention provides a means for modifying existing polyester polymers to optimize characteristics for solid state polymerization and for utilization in a wide array of specific applications. For instance, the modification technique of this invention may be used to adjust the melting point, crystallization temperature (either from the solid or on cooling from the melt), glass transition temperature, natural stretch ratio, barrier properties, melt strength, and/or solid state polymerization characteristic of the polyester. Application of the instant invention could result in a polymer with substantially different physical properties, potentially allowing modification of commodity resins for use in heretofore high cost, specialty applications. A further advantage of the invention is that recycled polymer may be modified to broaden its potential uses into more demanding higher performance applications.

This is a continuation-in-part of U.S. patent application Ser. No.16/277,550, filed on Feb. 15, 2019, which claims priority to U.S.Provisional Patent Application Ser. No. 62/702,118, filed on Jul. 23,2018. The teachings of U.S. patent application Ser. No. 16/277,550 andU.S. Provisional Patent Application Ser. No. 62/702,118 are incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to the modification of a polyester polymer afterthe completion of melt polymerization. The polymers to be modified bythis invention typically have an intrinsic viscosity (IV) of at leastabout 0.4 dL/g or a number average molecular weight (M_(n)) of at leastabout 10,000 daltons or a degree of polymerization (DP) of at leastabout 50. This modification may be undertaken to affect the physicalproperties of the final polymer including but not limited to the meltingpoint, crystallization temperature either from the solid or on coolingfrom the melt, glass transition temperature, natural stretch ratio,barrier properties, and melt strength.

BACKGROUND OF THE INVENTION

Polyester resins, especially polyethylene terephthalate (PET or PETE)and its copolymers have become ubiquitous. While PET is the mostcommonly encountered and recognizable polyester resin, several othershave achieved a high degree of importance or use. Polybutyleneterephthalate (PBT) is an important engineering resin with a variety ofuses in electrical applications, molded parts and specialty fibers amongothers. Polytrimethylene terephthalate (PTT) has also beencommercialized and promoted as a specialty fiber with improvedproperties over PET. Polyethylene naphthalate (PEN) is a specialty resinwith improved gas barrier performance, higher strength, glass transitiontemperature (Tg), and melting point than PET and finds use in severalmarkets as diverse as reinforcement for high speed tires and returnable,refillable bottles.

The aliphatic diacids have also been reacted with a variety of aliphaticdiols to prepare the corresponding aliphatic polyesters as exemplifiedby polyethylene adipate (PEA), polyethylene succinate (PES),polybutylene adipate (PBA) and polybutylene succinate (PBS). In general,the hydrolytic stability and physical properties of these are much lowerthan those of polyesters based on aromatic diacids and thus, they havefound only niche applications.

A third class of polyester resins, similar to the aliphatic polyestersdiscussed immediately above, can be produced from molecules containingboth a carboxylic acid and a hydroxyl group. In principle, at least, thechemistry of polymerization is the same as that for the production ofpolyester resins from a diacid and a diol—a hydroxyl group on onemolecule reacts with a carboxylic acid group on a second molecule toform an ester and by-product water. Several polymers of this type havebeen commercialized including the simplest—polyglycolic acid (PGA),polylactic acid (PLA) and polycaprolactone (PCL). While all thealiphatic acid based polyester resins have poor hydrolytic stabilityrelative to PET, they have found significant uses. They arebiodegradable, and so all three mentioned are being utilized for medicalapplications such as absorbable sutures and implants. PGA and PLA arealso finding use in container applications because of their better gasbarrier properties vs. PET and their biodegradability.

The polyester resins derived from aromatic acids, especially in theirsemi-crystalline state, are particularly useful being relatively inert.This is witnessed by their varied use as containers for as diversematerials as liquid soaps and shampoos, acidic foodstuffs such ascondiments, salad dressings and fruit juices, alcoholic beverages andalcohol based hand sanitizers. Some foodstuffs are hot filled attemperatures close to the boiling point of water or are pasteurizedafter filling. Still other PET resins are used as containers for foodsthat can be cooked in a microwave oven or are baked in a conventionaloven at temperatures up to 425° F. (218° C.). Polyesters containingnaphthalene-2, 6-dicarboxylic acid (NDA) residues have even higher usetemperatures and resistance to other agents.

Most commercial polyester resins are produced in large scale continuouspolymerization reaction systems in which a diacid, usually eitherterephthalic acid (TPA) or naphthalene-2,6-dicarboxylic acid (NDA) ortheir dimethyl esters are reacted with ethylene glycol (EG),trimethylene glycol, 1,4-butane diol (BDO), 1,4-cyclohexanedimethanol(CHDM), or 2,2,4,4-tetramethyl-1,3-cyclobutanediol. Water (or methanoland excess glycol) are continuously removed to drive thepolycondensation polymerization reaction. Small amounts of otherco-monomers are often added to the polymerization recipe in order tomodify the physical properties of the resulting resin. These co-monomersmay include but are not limited to isophthalic acid (IPA), salts ofsulfoisophthalic acid, phthalic acid, trimesic acid, trimellitic acid,pyromellitic acid, cyclohexane-1,4-dicarboxylic acid,cyclohexanediacetic acid, diphenyl-4,4′-dicarboxylic acid,naphthalene-2,6-dicarboxylic acid, diethylene glycol, triethyleneglycol, tetraethylene glycol, polyethylene glycol, polyethylene glycolco-propylene glycol, 1,4-cyclohexanedimethanol,hydroquinone-bis-(2-hydroxyethyl)ether, neopentyl glycol, glycol estersof lithium or sodium sulfoisophthalic acid, trimethylolpropane,pentaerythritol, other modifying glycols having 5 to 16 carbons, orethylene glycol, trimethylene glycol, 1,4-butane diol, and2,2,4,4-tetramethyl-1,3-cyclobutanediol. In a few cases, relativelylarge quantities of co-monomers may be added, examples of which includesome terephthalate/2, 6-naphthalate co-polymers exemplified by theHiPerTuf™ polymers which had been marketed by Shell Chemical, highCHDM-containing TPA based polymers generically known as PETGco-polymers, and a series of TPA/bio-based aliphatic diacids polymerizedwith BDO manufactured by Novamont under the Origo-Bi® tradename.

Polyester manufacture has moved toward larger and larger polymerizationlines to increase efficiency and in turn to reduce cost. These largepolymerization lines typically consist of several chained reactors whichoperate under different conditions of temperature and pressure to effectesterification and eventually polycondensation to build higher molecularweight polyester resin. Total residence time in this reactor chain istypically on the order of 3 to 4 hours resulting in 8 to 12 hours ormore needed to effect a change from one polymer composition to another.These polymerization lines typically produce 50 to 100 thousand poundsof polymer per hour resulting in significant losses during resintransitions as the polymer produced during the change can at best berecycled to recover the raw material value. This has resulted in themanufacturing process becoming less flexible with it being increasinglymore problematic and impractical to change the composition of thepolyester to meet particular desired physical characteristics. In otherwords, current large scale manufacturing techniques are less suitablefor making specialty polyesters having desired physical characteristicswhich are needed or desirable for use in various applications. Forinstance, specialty polymers which are modified with additional monomersto attain desired characteristics cannot be made efficiently in suchlarge scale operations and are typically made in small scale operationsat substantially higher cost. In contrast to the usual meltpolymerization of the entire polymer recipe, the instant invention addsspecialty monomers after the main constituents desired in the polymer,which likely represents a commodity resin, have been polymerized,shortly before the intermediate melt polymer is pelletized.

In practice, it is difficult to carry out melt polymerization for asufficient length of time to build the molecular weight desired for thefinal product because it becomes progressively more difficult to removeby-products from the molten resin and the power requirements to mix itbecome increasingly high. Also, side reactions leading to degradation ofthe polymer begin to become significant. These problems are avoided inthe case of crystallizable resins by utilizing a process of solid statepolymerization (SSP). The intermediate molecular weight resin isconverted to a pellet form, crystallized and then heated at atemperature slightly below where it begins to melt and subjected eitherto vacuum or inert gas purge to remove polymerization by-products.

It is possible to react glycols or polyol co-monomers with polyesters,such as those made in large scale facilities. However, in doing so thepolymer chain of the polyester is cleaved and consequently the molecularweight of the polyester is reduced and its associated physicalproperties also changed (frequently in an undesirable manner). Theinsertion of a glycol or polyol into the polyester chain is analogous tothe hydrolysis reaction, the reverse of the polymerization reaction, butwith the difference being in that instead of regenerating an acid endgroup and an alcohol end group, two alcohol end groups are generated.This difference significantly affects the ability to rebuild molecularweight either through conventional solid state polymerization (SSP) orunder vacuum in the melt.

The generation of two alcohol end groups on cleavage of a polyesterchain by a glycol or polyol is deleterious to the ability to rebuildchain length or molecular weight for several reasons. Among the moreimportant is the decrease of catalytic activity relative to the initialpolymerization conditions. The chain building or polymerizationreactions important in conventional polyester polymerization arecatalyzed by acid. This may be either a proton as from the carboxylicacid end groups or by catalysts, such as compounds of antimony (Sb),titanium (Ti), iron (Fe), zinc (Zn), germanium (Ge) and the like, whichare added or generated in situ from the metal. A second effect ofpolyester chain cleavage by a glycol or polyol on rebuilding molecularweight is that by-product removal becomes more difficult.

In the esterification polymerization reaction in which a carboxylic acidend group reacts with an alcohol end group, the by-product is water, asmall, relatively volatile compound which can vaporize from the polymerand be removed. Alternatively, the reaction of two chain ends, both ofwhich are alcohols, a transesterification reaction, produces as aby-product a glycol or polyol. These glycol or polyol molecules are muchmore difficult to remove from the reacting polymer and can cleave thegrowing polyester chain again resulting in no net change in polymermolecular weight.

To attain fast polymerization rates and to reach high molecular weightsin solid state polymerizations to it important for the ratio of carboxylend groups to hydroxyl end groups in the polyester being polymerized tobe in an optimal range. This optimum will vary with the type of solidstate polymerization reactor being utilized. The importance of thisratio in solid state polymerizations which are conducted in static bedreactors is described by Duh in U.S. Pat. No. 4,238,593. Morespecifically, Duh describes a method for the production of a highmolecular weight, high purity polyester comprising the steps of (a)reacting a glycol and a dicarboxylic compound selected from the groupconsisting of dicarboxylic acids and dicarboxylic esters to form apolyester prepolymer having an intrinsic viscosity from about 0.40 dl/gto about 0.62 dl/g and having a carboxyl end group content from about18% to about 40% of total end groups, said dicarboxylic acids selectedfrom the group consisting of alkyl dicarboxylic acids having a total offrom 2 to 16 carbon atoms, and aryl dicarboxylic acids containing atotal of from 8 to 16 carbon atoms, said dicarboxylic esters selectedfrom the group consisting of alkyl esters having from 4 to 20 carbonatoms and an alkyl substituted aryl ester having from 10 to 20 carbonatoms, said glycol selected from the group consisting of glycols having2 to 10 carbon atoms, and (b) polymerizing in a solid state in a staticbed, said polyester prepolymer so that a high molecular weight, highpurity polycondensed polyester is formed, said polycondensed polyesterhaving an intrinsic viscosity of at least 0.70 dl/g and having anacetaldehyde impurity concentration less than about 3.0 parts permillion.

In many cases there is a need to modify polyesters made by meltpolymerization to optimize solid state polymerization characteristicsfor a particular type of solid state polymerization reactor. There isalso a need to modify preexisting polyesters from various sources toadjust their physical properties to attain specific requirements. Thisis particularly true in cases where the polyester having the neededcharacteristics is simply not available or is too costly. There is alsoa long felt need for a technique to modify recycled polyester, such aspolyethylene terephthalate (PET) from recycled beverage bottles, to makeit suitable for higher performance application than those in which it iscurrently used, such as in strapping or fiberfill.

SUMMARY OF THE INVENTION

The subject invention provides a means for modifying existing polyesterpolymers to optimize characteristics for solid state polymerization andfor utilization in a wide array of specific applications. For instance,the modification technique of this invention may be used to adjust themelting point, crystallization temperature (either from the solid or oncooling from the melt), glass transition temperature, natural stretchratio, barrier properties, melt strength, and/or solid statepolymerization characteristic of the polyester. Application of theinstant invention could result in a polymer with substantially differentphysical properties, potentially allowing its use in heretofore highcost, specialty applications. A further advantage of the invention isthat recycled polymer may be modified to broaden its potential uses intomore demanding, higher performance applications.

The present invention more specifically discloses a method for modifyinga polyester polymer, comprising reacting (a) the polyester polymer (b) afirst compound which has at least two reactive groups which are selectedfrom the group consisting of hydroxyl groups, primary amine groups, orsecondary amine groups and (c) a second compound which has at least tworeactive groups capable of reacting with the reactive groups of thefirst compound to produce a modified polyester polymer, wherein saidmethod is conducted in the melt phase, and wherein the polyester polymerhas an intrinsic viscosity of at least about 0.40 dL/g as measured at25° C. in a solvent consisting of 60 weight percent phenol and 40 weightpercent tetrachloroethane.

The subject invention further reveals a method for modifying a polyesterpolymer comprising reacting the polyester polymer with a hydroxysubstituted carboxylic acid to produce a modified polyester polymer,wherein said method is conducted in the melt phase, and wherein thepolyester polymer has an intrinsic viscosity of at least about 0.40 dL/gas measured at 25° C. in a solvent consisting of 60 weight percentphenol and 40 weight percent tetrachloroethane.

The present invention also discloses a method for modifying a polyesterpolymer comprising reacting the polyester polymer with a hydroxysubstituted carboxylic acid to produce a modified polyester polymer,wherein said method is conducted in the melt phase, wherein thepolyester polymer is modified with less than 5 mole percent of thehydroxyl substituted carboxylic acid based upon the total number ofrepeat units in the polyester polymer, and wherein the modifiedpolyester polymer has an intrinsic viscosity of at least about 0.30 dL/gas measured at 25° C. in a solvent consisting of 60 weight percentphenol and 40 weight percent tetrachloroethane. The hydroxy substitutedcarboxylic acid can be a member selected from the group consisting ofglycolic acid and lactic acid and the polyester polymer can bepolyethylene terephthalate. The polyester polymer can be modified withless than 4 mole percent, 3 mole percent, 2 mole percent, 1 molepercent, 0.5 mole percent, 0.2 mole percent, 0.1 mole percent, or even0.05 mole percent of the hydroxyl substituted carboxylic acid, basedupon the total number of repeat units in the polyester polymer. In oneembodiment of this invention the hydroxyl substituted carboxylic acid isadded to the polyester polymer as it is being extruded. The modifiedpolyester polymer will typically have an intrinsic viscosity of at least0.35 dL/g, 0.40 dL/g, 0.45 dL/g, or 0.50 dL/g as measured at 25° C. in asolvent consisting of 60 weight percent phenol and 40 weight percenttetrachloroethane. In the practice of this invention the polyesterpolymer is not added sequentially or in stages.

The subject invention further reveals a method for modifying a polyesterpolymer, comprising reacting (a) the polyester polymer having anintrinsic viscosity of at least 0.40 dL/g as measured at 25° C. in asolvent consisting of 60 weight percent phenol and 40 weight percenttetrachloroethane, (b) a first compound which has at least two reactivegroups which are selected from the group consisting of hydroxyl groups,primary amine groups, or secondary amine groups and (c) a secondcompound which has at least two reactive groups capable of reacting withthe reactive groups of the first compound to produce a modifiedpolyester polymer, wherein said method is conducted in the melt phase,wherein the modified polyester polymer is modified with less than 5 molepercent of the first compound based upon the total number of repeatunits in the polyester polymer, wherein the modified polyester polymeris modified with less than 5 mole percent of the second compound basedupon the total number of repeat units in the polyester polymer, andwherein the modified polyester polymer has an intrinsic viscosity of atleast 0.30 dL/g as measured at 25° C. in a solvent consisting of 60weight percent phenol and 40 weight percent tetrachloroethane. In thisprocess the first compound and the second compound are added to thepolyester polymer as it is being extruded and the polyester polymer isnot added sequentially or in stages. The modified polyester polymertypically modified with less than 5 mole percent, 4 mole percent, 3 molepercent, 2 mole percent, 1 mole percent, 0.5 mole percent, 0.2 molepercent, 0.1 mole percent, or 0.05 mole percent of the first compound,based upon the total number of repeat units in the polyester polymer,and the modified polyester polymer is modified with less than 5 molepercent, 4 mole percent, 3 mole percent, 2 mole percent, 1 mole percent,0.5 mole percent, 0.2 mole percent, 0.1 mole percent, or 0.05 molepercent of the second compound based upon the total number of repeatunits in the polyester polymer. The polyester polymer is frequentlypolyethylene terephthalate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the effect of added branching on the meltrheology of the resins in accordance with this invention as described inExample 1.

DETAILED DESCRIPTION OF THE INVENTION

Virtually any type of polyester can be modified in accordance with themethod of this invention. The polyester can be made by conventional meltpolymerization or it can be made by a combination of melt polymerizationfollowed by solid state polymerization. The production of polyester byconventional melt polymerization is described in U.S. Pat. No.3,551,386. The teachings of U.S. Pat. No. 3,551,386 are incorporatedherein by reference for the purpose of teaching such a conventional meltpolymerization technique. The polyesters modified in accordance withthis invention are typically synthesized by the condensationpolymerization of a dicarboxylic acid or a dicarboxylic ester with aglycol. The dicarboxylic acids may be an alkyl and contain a total offrom 2 to 15 carbon atoms. Preferably, the acids are aryl or an alkylsubstituted aryl containing from about 8 to about 16 carbon atoms.Specific examples of alkyl dicarboxylic acids include oxalic acid,malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, and the like. Specificexamples of an aryl acid include the various isomers of phthalic acid,such as paraphthalic (terephthalic) acid and isophthalic acid, andnaphthalene dicarboxylic acid. Lithium sulfoisophthalic acid, sodiumsulfoisophthalic acid, glycol esters of lithium sulfoisphthalic acid,and glycol esters of sodium sulfoisphthalic acid are often preferred.Specific examples of alkyl substituted aryl acids include the variousisomers of dimethylphthalic acid, such as dimethylisophthalic acid,dimethylorothophthalic acid and dimethylterephthalic acid; the variousisomers of diethylphthalic acid, such as diethylisophthalic acid,diethylorthophthalic acid and diethylterephthalic acid; the variousisomers of dimethylnaphthalene dicarboxylic acid, such as2,6-dimethylnaphthalene dicarboxylic acid and 2,5-dimethylnaphthalenedicarboxylic acid; and the various isomers of diethylnaphthalenedicarboxylic acid. Generally, dimethylterephthalic acid is preferredwith terephthalic acid being highly preferred.

In lieu of the various dicarboxylic acids, the various esters thereofmay be utilized. Thus, the dicarboxylic compound may be an alkyl estercontaining a total of from about 4 to 20 carbon atoms, as well as alkylsubstituted aryl esters containing from about 10 to about 20 carbonatoms may be utilized. Examples of specific alkyl diesters includedimethyladipate, diethyladipate, and the like. Specific examples ofvarious alkyl substituted aryl diesters include the various isomers ofdimethylphthalate, the various isomers of diethylphthalate, the variousisomers of dimethylnaphthalate, and the various isomers ofdiethylnapthalate. Preferably, the various isomers of dimethylphthalate(dimethylterephthalate) are used.

These carboxylic acids or the esters thereof react in the esterificationprocess with a glycol containing from about 2 to 10 carbon atoms. Theglycols may be straight-chained or branched. Specific examples includeethylene glycol, propylene glycol, trimethylene glycol, 1,2-butane diol,1,3-butane diol, 1,4-butane diol, 2,3-butane diol, neopentyl glycol,1,4-cyclohexanedimethanol and the like. Of the various glycols, thosehaving from 2 to 8 carbon atoms are preferred, with ethylene glycol and1,4-butane diol being highly preferred.

A variety of modifications to the melt polymerization process, usedeither alone or in combination, can be utilized to achieve a meltpolymer with the optimal carboxyl content. When dicarboxylic acids andglycol are used as the precursors, the polyester prepolymer can beprepared with or without the use of a heel to speed up theesterification of the acid. The heel is an esterification productrecycled to be used to increase the solubility of the dicarboxylic acidand thereby increase the reaction rate of the dicarboxylic acid in theglycol. The use of a heel is explained in U.S. Pat. No. 4,020,049 and inU.S. Pat. No. 3,427,287. The teachings of U.S. Pat. No. 4,020,049 and inU.S. Pat. No. 3,427,287 are both incorporated herein by reference forthe purpose of teaching melt polymerization techniques that are suitablefor use in synthesizing polyesters by melt polymerization.

When a heel is not used, the glycol/dicarboxylic acid molar charge ratiois usually about 1.2:1.0 or greater because a lower charge ratio willcause agitation and mixture difficulties. With this ratio, the polyesterprepolymer produced will have a carboxyl content far lower than theoptimal value and the prepolymer will have a lower reaction rate in thesubsequent solid state polymerization. To optimize the carboxyl contentof the polyester prepolymer, make-up dicarboxylic acid can be addedafter partial completion of the esterification of the acid. While it ispossible to add the make-up dicarboxylic acid at any time during thelater stages of the esterification of the acid, it is desirable to addthe make-up acid after approximately 90%-95% of the acid has beenesterified. The amount of make-up dicarboxylic acid to be added is suchthat the overall glycol to acid molar charge ratio is from about1.02:1.0 to about 1.15:1.0, and preferably within 1.03:1.0 to about1.10:1.0. In cases where terephthalic acid is used as the dicarboxylicacid, the charge ratio is preferably within the range of about 1.03:1.0to 1.10:1.0.

When a heel is used, the heel is first produced by reactingapproximately 1.20 moles of glycol with 1.0 moles of dicarboxylic acid.After the esterification of the acid is approximately 95% complete,make-up dicarboxylic acid is added to the heel to adjust the overallglycol/acid molar ratio in the heel to be from about 1.02:1.0 to about1.15:1.0, the desired molar ratio. After the new heel with the desiredmolar ratio is esterified within approximately 90%-95% of completion, abatch having from about 1.02:1.0 to about 1.15:1.0 glycol/acid ratio canbe charged into the vessel containing the heel. Because of the presenceof the heel having the desired molar ratio, there will be no agitationproblem with the low glycol/acid charge ratio.

The partial melt process utilizing the dicarboxylic acid, as modified toachieve the low glycol/acid molar ratio, may be carried out underatmospheric or super atmospheric pressures at temperatures between about240° C. to about 290° C. If a dicarboxylic ester is used in place of thedicarboxylic acid, no heel is needed for the reaction between the glycoland the dicarboxylic ester, denominated the ester exchange reaction. Anester exchange catalyst, such as manganese (Mn), zinc (Zn), and/ortitanium (Ti) is typically needed. The polyester prepolymer producedfrom the dicarboxylic ester invariably has a very low carboxyl numberwhich has been found to polymerize very slowly in the subsequent solidstate polymerization. Again, the carboxyl content of the prepolymer maybe optimized by the addition of dicarboxylic acid, in this case for thefirst time. Because a higher glycol/dicarboxylic ester charge ratiowhich is within the range of 1.80:1.0 to 2.20:1.0 is usually used, thedicarboxylic acid can be charged initially with the dicarboxylic esterand the glycol or added after a partial completion of the ester exchangereaction. It has been found that, when using terephthalic acid,dimethylterephthalate, and ethylene glycol, that it is preferred to addthe terephthalic acid after the completion (from about 95% to about100%) of the ester exchange reaction. The molar ratio of dicarboxylicacid to dicarboxylic ester is from about 0.05:1.0 to about 0.50:1.0, andpreferably from about 0.10:1.0 to about 0.30:1.0. Whenever terephthalicacid and dimethylterephthalate are used in the preferred embodiment, themolar ratio is preferred to be from about 0.10:1.0 to about 0.30:1.0.

The ester exchange reaction is conducted at atmospheric pressures and attemperatures from about 180° C. to about 250° C. After completion of theester exchange reaction and the addition of the dicarboxylic acidaccording to the preferred method, a polycondensation catalyst, such asantimony (Sb) or titanium (Ti), is added, and the mixture is permittedto react for approximately 10 to 30 minutes.

Whether prepared using the dicarboxylic acid or the dicarboxylic ester,the melt process then enters the partial vacuum stage wherein theatmospheric or super atmospheric pressures of the esterification stageis reduced to sub-atmospheric pressures. A condensation reactioncatalyst is added to the polymer made from the dicarboxylic acid tobegin the partial polycondensation. The addition of the polycondensationcatalyst, whether it be antimony (Sb), titanium (Ti), iron (Fe), zinc(Zn), cobalt (Co), lead (Pb), manganese (Mn), niobium (Nb), or germanium(Ge), is preferably added to the partial melt process prior to thereduction of the atmospheric pressure to sub-atmospheric pressure. Thepolycondensation reaction continues after pressure has reached a fullvacuum of approximately less than 5.0 and preferably less than 1.0millimeters of mercury, until the desired intrinsic viscosity of between0.35 dl/g and 0.62 dl/g is reached. The desired polycondensationreaction temperature during the imposition of a partial, and later, afull vacuum is within the range of about 260° C. to 290° C. andpreferably within the range of 270° C. to 285° C.

The polyester is then typically solidified, pelletized or diced forutilization in manufacturing product or for further processing, such asby solid state polymerization or for modification in accordance withthis invention. In cases where higher molecular weight than caneffectively be produced (or can be made) by melt polymerization isdesired the polyester (sometimes referred to as the prepolymer) issubsequently solid state polymerized to the higher molecular weight.According to the requirements for the size of the prepolymer particles,the pelletizing or dicing processes may produce a usable particle sizebetween about a cube having ⅛ inch sides and a particle to be retainedby 20 mesh. Desirably, the particles may pass through 6 mesh and beretained by 12 mesh. Preferably, the particles may pass through 8 meshand be retained by 10 mesh. The mesh values are determined according tothe Tyler Mesh Classification System.

In cases where solid state polymerization is utilized the polyester istransferred to a solid state polymerization reactor for solid statepolymerization in a fluidized bed, static bed, a modified static bed, aninclined cylindrical rotating reactor or under conditions of forcedmotion (such as in a blender dryer). The static bed solid statepolymerization is preferred because of its lower energy requirements.Typically, catalysts such as antimony, titanium, iron, zinc, cobalt,lead, manganese, niobium, and germanium are utilized increasepolymerization rates. It is typically preferred to utilize an antimonyor a titanium catalyst with titanium generally being most preferred.U.S. Pat. No. 4,238,593 reveals a solid state polymerization which iscarried out in a static bed reactor. The teachings of U.S. Pat. No.4,238,593 are incorporated herein by reference for the purpose ofdisclosing a solid state polymerization technique which is suitable formaking polyester which can be modified in accordance with thisinvention.

U.S. Pat. No. 8,790,580 described the use of an inclined cylindricalrotating reactor in the solid state polymerization of polyester. In theprocess disclosed by this patent the inclined cylindrical rotatingreactor comprising an axis of rotation, granules of polyester treatedwithin the reactor, a granules of polyester flow regime, at least twomixing devices and an inert purge gas, for the solid statepolymerization of the granules of polyester, wherein the granules ofmaterial treated within the reactor comprise a polyester and the reactorhas a temperature in the range of about 140° C. to about 235° C., theaxis of rotation is central and not parallel to the horizontal lineperpendicular to the force of gravity, the granules of polyester flowregime is characterized by a Froude Number Fr=(ω²×R/g) comprised in therange of 1×10⁻⁴ to 0.5; where w is the angular velocity of the reactor;R is the internal radius of the reactor and g is the gravity ofacceleration=9.806 m/s; and each of the at least two mixing devices hasa height, width, and an equivalent length defined as the distancebetween the plane perpendicular to the axis of rotation that containsthe point where the mixing device first protrudes from the reactor walland the plane perpendicular to the axis of rotation that contains thepoint where the mixing device stops protruding from the wall and theequivalent length of the mixing device is selected from the groupconsisting of equivalent lengths less than 1/10^(th) the length of thereactor, so as the granules of the polyester treated within the reactorpass through the reactor due to the force of gravity as well as thereactor rotation with a plug flow like behavior; and the at least twomixing devices are connected in a manner so that the inert purge gas canpass from the first mixing device to the second mixing device through aconnector; said use comprising the steps of: introducing the granulesinto the top of the reactor passing the granules through the reactorwhile subjecting the granules to a stream of inert purge gas below theturbulent rate.

The modification technique of this invention can be employed to modifyvirgin polyester or polyester from recycle streams. This modification iscarried out by melting the polyester and mixing a first compound whichhas at least two reactive groups which are selected from the groupconsisting of hydroxyl groups, primary amine groups, or secondary aminegroups and a second compound which has at least two reactive groupscapable of reacting with the reactive groups of the first compoundtherein. The first compound is typically added to the molten polyesterprior to adding the second compound. However, the two compounds can beadded in either order or added to the molten polyester simultaneously.This modification procedure can be carried out in any vessel which iscapable of maintaining the polyester above its melting point and whichis equipped to provide adequate mixing of the first compound and thesecond compound throughout the polyester being modified. For instance,the reaction can be conducted in an extruder, such as an extruder havingmultiple mixing and heating zones.

Various salts of phosphonated dicarboxylic acids and polycarboxylicacids as well as sulfonated dicarboxylic acids and polycarboxylic acidsare useful for modifying polyesters to achieve the purpose of creating acompatibilizing polymer, improving the dyability of a polymer,increasing its hydrophilicity, incorporation of a bactericide and thelike. Examples of such polymer modifying agents may be found in numerousUnited States patents and United States Patent ApplicationsPublications, including U.S. Pat. Nos. 9,193,677, 7,943,216, 7,928,150,6,692,671, 6,525,165, 6,479,619, 5,472,831, and United States PatentApplication Publication No. 2012/0207955. The teachings of U.S. Pat.Nos. 9,193,677, 7,943,216, 7,928,150, 6,692,671, 6,525,165, 6,479,619,5,472,831, and United States Patent Application Publication No.2012/0207955 are incorporated herein by reference for the purpose ofdescribing such salts and the benefits of modifying polyesterstherewith. Particularly useful are salts of the varioussulfobenzenedicarboxylic acids including 4-sulfophthalic acid,sulfoterephthalic acid, 5-sulfoisophthalic acid,4-sulfonaphthalene-2,7-dicarboxylic acid, and4-sulfonaphthalene-2,6-dicarboxylic acid and 2-sulfosuccinic acid.Depending upon the intended application, a variety of cations are usefulcounter ions.

Particularly useful in many applications are the lithium, sodium,potassium, zinc, magnesium, calcium, cobalt, and silver salts as well asquaternary phosponium salts such as tetrabutylphosphonium,benzyltributylphosphonium, tetraphenylphosphonium and the like. Any ofthese sulfocarboxylic acids may be incorporated as polymer modifyingagents as the free carboxylic acid, or as bis- or mono-ester wherein thealcohol used to create the ester function still has a free hydroxylgroup available for further esterification reaction.

Lithium bis-2-hydroxyethyl-5-sulfoisophthalate may be prepared as anethylene glycol solution as described in U.S. Pat. Nos. 9,193,677 and6,479,619 or simply by heating lithium sulfoisophthalate, withsufficient ethylene glycol to yield a final concentration of 40%bis-ester, at a temperature within the range of 170° C. to 185° C. withremoval of water as a by-product. After completion of esterification,the resulting solution can be filtered and cooled. Dry lithiumbis-2-hydroxyethyl-5-sulfoisophthalate may be obtained by pouring 100 gof the cooled solution into 1.5 L acetone with stirring. The acetone/EGsolution can be decanted off the resulting oil and the oil treated 2times with an additional 0.5 L of acetone with them being stirredtogether for 1 hour each. After decanting off the acetone wash, the oilcan be dried in a vacuum oven at a temperature of 50° C. for 20 hoursand then broken up and powdered. Other S2-hydroxyalkyl sulfocarboxylatesmay be similarly prepared for instance by use of 1,3-propane diol or1,4-butane diol in place of ethylene glycol.

Test Methods Intrinsic Viscosity

The intrinsic viscosity (IV) of the polymer samples was measured as 0.5%solutions in 60/40 w/w phenol/tetrachloroethane in accordance with ASTMMethod D 4603 using a Rheotek RPV-1 automatic viscometer fitted with anUbbelohde 1B viscometer. Solution flow time relative to that of the puresolvent was measured, relative viscosity determined and intrinsicviscosity calculated using the Billmeyer equation with intrinsicviscosity values being reported in units of dL/g.

Carboxyl Number (Milliequivalents COOH End Groups/10⁶ g Polymer)

In determining the carboxyl number of polyester samples approximately0.1 g of polymer was dissolved in 5 mL of dry nitrobenzene at 200° C.Then, 5 mL of benzyl alcohol and 2 drops phenol red indicator wereadded. The solution was then subsequently titrated to a blue endpointusing a standard sodium hydroxide/benzyl alcohol solution.

Thermal Properties

The melting points (Tm) and glass transition temperatures (Tg) of thepolymer samples were determined using a TA Instruments Model Q2000 DSC.Heating and cooling rates for measurements were set at 10° C./minute.

Melt Rheology

The melt rheology of polymers was determined using a Dynisco Model 7000polymer test system. Polymer samples were dried overnight in a vacuumoven at 120° C. and were then loaded into the rheometer at 280° C. undera nitrogen blanket. After preheating at the test temperature for 5minutes, samples were extruded through a stainless steel capillary diewhich was 25.4 mm long, 0.762 mm in diameter and which had a 120°conical entrance angle. Shear rates were varied from 10 to 2000 sec⁻¹ byvarying the crosshead speed. For comparative purposes, CLEARTUF® MAX™polyester resin was also included in this study.

Example 1 Addition of Pentaerythritol (and Isophthalic Acid) to PostConsumer Recycle

Mixed post-consumer recycle PET (PCR) flake from various sources wasground to pass through a 5 mm screen. This material (˜30 lbs.) was mixedto produce a uniform blend. A solution of 1.2 grams of pentaerythritol(PE) (0.075 mol % ethylene glycol (EG) equivalents) in 300 mL methanolwas added to 4500 grams of the blended PCR flake in a 5 gallon bucket.The bucket was sealed and placed on a roller for 2 hours to uniformlycoat the PCR flake with PE. The bucket was then removed from the roller,unsealed and dried in a vacuum oven overnight applying full vacuum at atemperature of 160° C. After drying, 1500 g of PE treated flake wasremoved and blended in a sealed can on a roller with 1.8 g of powderedisophthalic acid (IPA). The PCR samples were extruded through a 27 mmLeistritz twin screw extruder (L/D=40) and pelletized to generatesamples 1 through 3 as described in Table I. Likewise, samples 5 and 6were prepared by increasing the PE to 3.4 g (0.2 mol % ethylene glycol(EG) equivalents) and the IPA to 5.2 g.

It was noted that the molecular weight as reflected in the IVmeasurement was relatively unaffected by the combination of the lowlevel of alkanolosis by the PE and its tetrafunctionality. This is shownby the generic equation below wherein R represents the continuation ofthe polymer chain or in the case of a polymer chain end a hydrogen atom,alkyl group, or substituted alkyl group, such as a hydroxy alkyl group.

However, water generated by esterification on the addition of IPA didresult in hydrolysis as illustrated below:

The polymer of the extruded samples had a resulting decreased molecularweight caused by the chain breaking reaction illustrated below:

After crystallizing in a hot air oven at 160° C., samples were solidstate polymerized in laboratory bench scale glass reactors. Samples weredried overnight under nitrogen flow at a temperature of 120° C. After 15hours the temperature was increased to 215° C. and maintained at thattemperature for an additional 5.5 hours after which the temperature wasagain increased to 225° C. for an additional 3.5 hours. Samples werewithdrawn periodically for measurement of intrinsic viscosity. Rates ofsolid state polymerization were significantly increased by the additionof IPA in an equimolar amount to the level of PE utilized.

Incorporation of the branched PE is further demonstrated by the meltviscosity of the polymers (FIG. 1). The PE containing, branched polymersshow the expected increased low shear viscosity and low high shearviscosity, that containing 0.2 mol % PE having nearly the same meltviscosity at an apparent shear rate of 2000/sec as Cleartuf® Max™polyester despite its 0.1 dL/g higher IV.

TABLE I Addition of Pentaerythritol and Isophthalic Acid toPost-Consumer Recycle in a Twin Screw Extruder COOH Run mol % PE mol %IPA IV (meq/10⁶ g) 1 0.625 50.9 2 0.075 0.637 46.3 3 0.075 0.075 0.59751.3 5 0.2 0.637 46.8 6 0.2 0.2 0.538 65.5

TABLE II Results of Solid State Polymerization of PentaerythritolModified Post-Consumer Recycle IV at_hrs Rate of IV increase sample 0 24 6 8 9 0-4 hrs 6-9 hrs 1 0.631 0.676 0.727 0.779 0.864 0.910 0.0240.044 2 0.646 0.706 0.754 0.819 0.896 0.964 0.027 0.047 3 0.606 0.6430.667 0.749 0.853 0.936 0.015 0.061 5 0.641 0.705 0.777 0.840 0.9071.004 0.034 0.052 6 0.550 0.575 0.620 0.703 0.796 0.909 0.018 0.066 Itshould be noted that the samples were dried overnight under nitrogenflow at 120° C. After 15 hours, the temperature was increased to 215° C.and maintained for 5.5 hours after which it was increased to 225° C.

FIG. 1 shows the effect of added branching on the melt rheology of theresins.

Example 2 Modification of Virgin Bottle Grade Polyester Resin

Cleartuf® 8006C polyester resin was dried in a vacuum oven overnight atfull vacuum at a temperature of 160° C. A molten, commercial grade of 1,4-cyclohexanedimethanol (30/70% cis/trans) 116 g was added to 7718 ghot, dry polymer in a 5 gallon can, sealed and placed on a roller for 1hour to uniformly coat the pellets. This was used to generate samples 9,10 and 12 by extrusion through the Leistritz extruder as in Ex. 1.Samples 10 and 12 additionally had solid glutaric acid and isophthalicacid respectively, added to the polymer melt through the use of anadditional feeder at a port about 12 diameters downstream of the feedthroat. Sample 8 is a control sample of Cleartuf® 8006C polyester resinextruded under the same conditions used for the rest of the experiment.

After extrusion, samples were crystallized in a hot air oven at 160° C.and solid state polymerized in lab bench glass reactors. Samples weredried for 2 hours under a nitrogen flow at a temperature of 180° C. Thetemperature was increased to 215° C. and maintained at that temperaturefor an additional 24 hours. Samples were withdrawn periodically for IVmeasurement. As can be seen in Table IV, rates of solid statepolymerization and final IV were significantly increased on addition ofeither acid in equimolar amounts to the CHDM.

TABLE III Modification of Virgin Cleartuf ® 8006C in a Twin ScrewExtruder Run mol % CHDM acid added mol % Acid IV COOH 8 0.709 41.2 9 2.00.295 42.5 10 2.0 glutaric 2.0 0.291 200.9 12 2.0 IPA 2.0 0.293 77.0

TABLE IV Results of Solid State Polymerization of CHDM ModifiedCleartuf ® 8006C init init COOH SSP time IV COOH rate of Tg mp2 Run IV(meq/10⁶ g) (hrs) final (meq/10⁶ g) IV inc (° C.) (° C.) 8 0.709 41.25.5 0.949 26.6 0.044 80.6 242 9 0.295 42.5 24 0.617 8.4 0.011 10 0.291200.9 24 0.899 32.7 0.022 77.5 235 12 0.293 77.0 24 0.772 22.9 0.01779.1 238

While the polymer produced in run 8 readily repolymerized to and beyondits starting IV, with a concomitant reduction in COOH end groups, theaddition of 2 mol % glycol in the form of CHDM substantially reduced themolecular weight but had no effect on the number of COOH end groups. Asa result, repolymerization was substantially retarded and even after 24hrs, only achieved an IV of 0.62 with the COOH end groups being reducedto just 8. In contrast, the melt addition of either glutaric acid orisophthalic acid, equimolar to the glycol added reduced the IV of theextrudate even further but with the desired increase of COOH end groupsand the ability to increase the molecular weight or IV of the resultingpolymers substantially above that achieved in their absence. Further,the rate of IV increase was about double that of the CHDM only sample.

Additional evidence of the incorporation of the CHDM and added diacidsin the polymer chain is seen in the reductions observed in both the Tgand the melting point of the repolymerized extrudates.

Example 3 Modification of Low IV Homopolymer

A low IV melt, homopolymer prepared from dimethyl terephthalate (DMT)and EG was dried overnight in a vacuum oven at a temperature of 160° C.After drying, 18.8 g (0.75 mol %) diethylene glycol (DEG) was added to4540 g of the dried polymer in a 5 gallon can, sealed and placed on aroller for 1 hour to uniformly coat the pellets. This was used togenerate samples 15 and 16 by extrusion through the Leistritz extruderas in Example 1. Sample 16 additionally had finely powdered isophthalicacid added to the polymer melt through the use of an additional feederat a port about 12 diameters downstream of the feed throat. Sample 14 isa control sample of the melt resin dried and extruded under the sameconditions used for the rest of the experiment.

After extrusion, samples were crystallized in a hot air oven at atemperature of 160° C. and then solid state polymerized in laboratoryscale bench glass reactors. Samples were dried for 2 hours under anitrogen flow at a temperature of 180° C. The temperature wassubsequently increased to 215° C. and maintained at that temperature for24 hours. Samples were withdrawn periodically for IV measurement. As canbe seen in Table VI, the solid state polymerization rate and final IVwere significantly increased on addition of IPA to the resin duringextrusion. As in Example 2, Tg and especially Tm were reduced byincorporation of the comonomers in the polymer chain.

TABLE V Modification of Low IV Homopolymer by DEG/IPA in a Twin ScrewExtruder Run mol % DEG mol % IPA IV COOH 14 0.438 25.0 15 0.75 0.35224.1 16 0.75 0.75 0.326 75.1

TABLE VI Results of Solid State Polymerization of DEG/IPA ModifiedHomopolymer init init COOH SSP time IV COOH rate of Tg mp2 Run IV(meq/10⁶ g) (hrs) final (meq/10⁶ g) IV inc (° C.) (° C.) 14 0.438 25.024 0.769 11.0 0.0109 80.5 252 15 0.352 24.1 24 0.637 8.9 0.0086 80.5 160.326 75.1 24 0.724 17.3 0.0146 80.3 249

While certain representative embodiments and details have been shown forthe purpose of illustrating the subject invention, it will be apparentto those skilled in this art that various changes and modifications canbe made therein without departing from the scope of the subjectinvention.

What is claimed is:
 1. A method for modifying a polyester polymercomprising reacting the polyester polymer with a hydroxy substitutedcarboxylic acid to produce a modified polyester polymer, wherein saidmethod is conducted in the melt phase, wherein the polyester polymer ismodified with less than 5 mole percent of the hydroxyl substitutedcarboxylic acid based upon the total number of repeat units in thepolyester polymer, and wherein the modified polyester polymer has anintrinsic viscosity of at least about 0.30 dL/g as measured at 25° C. ina solvent consisting of 60 weight percent phenol and 40 weight percenttetrachloroethane.
 2. The method for modifying a polyester polymer asspecified in claim 1 wherein the hydroxy substituted carboxylic acid isa member selected from the group consisting of glycolic acid and lacticacid.
 3. The method for modifying a polyester polymer as specified inclaim 1 wherein the modified polyester polymer is subsequently solidstate polymerized.
 4. The method for modifying a polyester polymer asspecified in claim 1 wherein the polyester polymer is modified with lessthan 4 mole percent of the hydroxyl substituted carboxylic acid, basedupon the total number of repeat units in the polyester polymer.
 5. Themethod for modifying a polyester polymer as specified in claim 1 whereinthe polyester polymer is modified with less than 3 mole percent of thehydroxyl substituted carboxylic acid, based upon the total number ofrepeat units in the polyester polymer.
 6. The method for modifying apolyester polymer as specified in claim 1 wherein the polyester polymeris modified with less than 2 mole percent of the hydroxyl substitutedcarboxylic acid, based upon the total number of repeat units in thepolyester polymer.
 7. The method for modifying a polyester polymer asspecified in claim 1 wherein the polyester polymer is modified with lessthan 1 mole percent of the hydroxyl substituted carboxylic acid, basedupon the total number of repeat units in the polyester polymer.
 8. Themethod for modifying a polyester polymer as specified in claim 1 whereinthe polyester polymer is modified with less than 0.5 mole percent of thehydroxyl substituted carboxylic acid, based upon the total number ofrepeat units in the polyester polymer.
 9. The method for modifying apolyester polymer as specified in claim 1 wherein the hydroxylsubstituted carboxylic acid is added to the polyester polymer as it isbeing extruded.
 10. The method for modifying a polyester polymer asspecified in claim 1 wherein the modified polyester polymer has anintrinsic viscosity of at least about 0.40 dL/g as measured at 25° C. ina solvent consisting of 60 weight percent phenol and 40 weight percenttetrachloroethane.
 11. A method for modifying a polyester polymer,comprising reacting (a) the polyester polymer having an intrinsicviscosity of at least 0.40 dL/g as measured at 25° C. in a solventconsisting of 60 weight percent phenol and 40 weight percenttetrachloroethane, (b) a first compound which has at least two reactivegroups which are selected from the group consisting of hydroxyl groups,primary amine groups, or secondary amine groups and (c) a secondcompound which has at least two reactive groups capable of reacting withthe reactive groups of the first compound to produce a modifiedpolyester polymer, wherein said method is conducted in the melt phase,wherein the modified polyester polymer is modified with less than 5 molepercent of the first compound based upon the total number of repeatunits in the polyester polymer, wherein the modified polyester polymeris modified with less than 5 mole percent of the second compound basedupon the total number of repeat units in the polyester polymer, andwherein the modified polyester polymer has an intrinsic viscosity of atleast 0.30 dL/g as measured at 25° C. in a solvent consisting of 60weight percent phenol and 40 weight percent tetrachloroethane.
 12. Themethod for modifying a polyester polymer as specified in claim 11wherein the polyester polymer is not added sequentially or in stages.13. The method for modifying a polyester polymer as specified in claim11 wherein the first compound and the second compound are added to thepolyester polymer as it is being extruded.
 14. The method for modifyinga polyester polymer as specified in claim 11 wherein the modifiedpolyester polymer is modified with less than 2 mole percent of the firstcompound based upon the total number of repeat units in the polyesterpolymer, and wherein the modified polyester polymer is modified withless than 2 mole percent of the second compound based upon the totalnumber of repeat units in the polyester polymer.
 15. The method formodifying a polyester polymer as specified in claim 11 wherein themodified polyester polymer is modified with less than 0.5 mole percentof the first compound based upon the total number of repeat units in thepolyester polymer, and wherein the modified polyester polymer ismodified with less than 0.5 mole percent of the second compound basedupon the total number of repeat units in the polyester polymer.
 16. Themethod for modifying a polyester polymer as specified in claim 11wherein the modified polyester polymer is modified with less than 0.2mole percent of the first compound based upon the total number of repeatunits in the polyester polymer, and wherein the modified polyesterpolymer is modified with less than 0.2 mole percent of the secondcompound based upon the total number of repeat units in the polyesterpolymer.
 17. The method for modifying a polyester polymer as specifiedin claim 11 wherein the modified polyester polymer is modified with lessthan 0.1 mole percent of the first compound based upon the total numberof repeat units in the polyester polymer, and wherein the modifiedpolyester polymer is modified with less than 0.1 mole percent of thesecond compound based upon the total number of repeat units in thepolyester polymer.
 18. The method for modifying a polyester polymer asspecified in claim 11 wherein the modified polyester polymer is modifiedwith less than 0.05 mole percent of the first compound based upon thetotal number of repeat units in the polyester polymer, and wherein themodified polyester polymer is modified with less than 0.05 mole percentof the second compound based upon the total number of repeat units inthe polyester polymer.
 19. The method for modifying a polyester polymeras specified in claim 11 wherein the modified polyester polymer ismodified with 0.075 mole percent to 2 mole percent of the first compoundbased upon the total number of repeat units in the polyester polymer,and wherein the modified polyester polymer is modified with 0.075 molepercent to 2 mole percent of the second compound based upon the totalnumber of repeat units in the polyester polymer.
 20. The method formodifying a polyester polymer as specified in claim 11 wherein themodified polyester polymer is subsequently solid state polymerized.